1. Field of the Invention
The present invention relates to a device comprising a semiconductor device, particularly relates to an evaluation method of the dopant density and the dopant activation rate in a semiconductor film, and provides a design management system (production management system) on which these things are taken into account. Further, the invention provides a program to make a computer obtain the dopant activation rate and control the dose amount.
2. Description of the Related Art
In a field effect transistor (hereinafter referred to as a ‘FET’), a thin film transistor (hereinafter referred to as a ‘TFT’), which is an example of FETs, and other semiconductor devices, the threshold voltage is an important parameter that decides the operating point. The threshold voltage is decided by the factors such as the activation rate of added dopant (impurity), (hereinafter referred to as the ‘dopant activation rate), and the distribution of carriers concentration (hereinafter referred to as ‘carrier density’).
In other words, it is necessary to control the dopant activation rate and the carrier density so that semiconductor devices obtain predetermined characteristics. The dopant activation rate is represented by the ratio of the amount of dopant which is actually activated to the amount of dopant which is added to a semiconductor film. The carrier density is the amount of carriers that actually flow in the channel region, which also varies depending on the presence of an applied voltage. Particularly, when the dopant activation rate is 100%, the dopant density and the carrier density are equal.
Conventionally, the carrier density is obtained by the Hall measurement, the CV measurement (capacitance measurement), or SIMS analysis.
As an example using SIMS analysis, which is a measurement of the above carrier density, there is a method such that: primary ions are emitted onto the surface of a conductive impurity-doped semiconductor film under the condition that the surface thereof is charged with electricity; the strength of the secondary ions having a specific energy emitted from the surface is sequentially measured with the elapse of emitting time of the primary ions; and, from the concentration of carriers corresponding to the strength of the secondary ions and the etching amount of the semiconductor film corresponding to the time of emitting of the primary ions, the carrier distribution in the depth direction in the semiconductor film is obtained (refer to Japanese Patent Laid-Open No. H7-66258).
It is difficult, however, to measure a thin film such as a TFT or SOI membrane by the Hall measurement. This is because, as the film is thinner, the resistance of the film is greater, and the Hall current is smaller, which makes it very difficult to obtain the carrier density. Particularly, in the case of a semiconductor device formed on a glass substrate, the CV measurement which requires grounding of the substrate is useless.
Further, the Hall measurement and the CV measurement require a specific TEG (Test Element of Groups) for measurement that is different from a device, and the carrier density of a TEG is measured. Since the TEG is produced under conditions different from the thermal history of the actual device process, it is possible that the carrier density and the dopant activation rate are different from those in the device.
Still further, with an actual device, the dopant density contributing to carriers (that is the activated dopant density) changes a lot with the state of the semiconductor film due to the high defect density in the film when the semiconductor film is non-crystal or polycrystal.
On the other hand, even a carrier density obtained from a singlecrystal wafer having a small defect density is not necessarily the same as the value of the actual device. This is because even if the dopant activation rate of the TEG is obtained by the Hall measurement, the CV measurement, or SIMS analysis, since the actual device goes through several thermal processes before completion, it is highly possible that the above obtained dopant activation rate is different from that in the semiconductor film of the device.
Further, to obtain the carrier density with high accuracy using the Hall measurement or the CV measurement, it is necessary to measure a maximum possible capacitance (in case of the CV measurement) or a maximum possible Hall current (in case of the Hall measurement). Therefore, the TEG for the Hall measurement or the CV measurement is much greater compared to the device. Consequently, since the obtained carrier density is an average value in a wide region, the dispersion of the values in a microscopic region cannot be evaluated.